1. Field of the Invention
This invention relates, in general, to a system for drying tobacco, and more particularly to a system for drying tobacco while providing for a minimal tobacco residence time in the drying apparatus.
2. Description of the Prior Art
Pneumatic tobacco conveyor dryer systems are known to the art. However, the dryer systems known to us have a number of drawbacks.
Three such systems are illustrated in U.S. Pat. No. 3,357,436 issued on Dec. 12, 1967 to A. H. Wright; U.S. Pat. No. 3,409,025 issued on Nov. 5, 1968 to W. Wochnowski; and U.S. Pat. No. 3,786,573 issued on Jan. 22, 1974 to John J. Scheppe and Raymond N. Carini.
U.S. Pat. No. 3,357,436 shows a tobacco drying apparatus having an air heater interconnected to a tobacco-air separator by means of a long duct forming a serpentine flow path, vertically oriented, drying chambers. The tobacco to be dried is introduced into the duct upstream of the serpentine flow path. As the heated tobacco bearing air flows upwardly through the drying chambers, the tobacco is dried.
U.S. Pat. No. 3,409,025 also shows a tobacco drying apparatus having an air heater interconnected to a tobacco-air separator by means of an inverted U-shaped duct. The tobacco to be dried is introduced into one of the vertical arms of the U-shaped duct downstream of the heater. The tobacco travels upwardly in this arm, changes direction through the bend of the duct and moves downwardly in the other arm to the separator device.
U.S. Pat. No. 3,786,573 illustrates a drying device having a heater interconnected to a separator by a long duct. Tobacco to be dried is introduced into this duct near the outlet from the heater. Controlled louvers are formed in the duct between the location whereby the tobacco is introduced and the entrance into the separator. The louvers are used to introduce a controlled amount of ambient air into the duct to control the temperature of the dried tobacco.
A common drawback of all of these systems is the extended residence time of the tobacco in the system. The longer the tobacco is kept in a system, the longer it is subjected to the drying effects of the air resulting in a chemical loss, particularly a loss of alkaloids.
A further drawback common to the apparatus of U.S. Pat. Nos. 3,357,436 and 3,409,025 is the curved or serpentine path which requires the tobacco bearing air to make directional changes as it moves to the separator. These directional changes have basically two disadvantageous effects. As the tobacco bearing air changes flow direction, some of the tobacco will be centrifuged out of the air stream. At least some of this centrifuged tobacco will build up along the curved walls of the duct, necessitating a cleaning of the duct from time to time to avoid clogging. Furthermore, the directional changes in the flow of the tobacco bearing air causes the tobacco to, at least partially, break-up.